Microsatellite Instability-high-positive Cancer of Unknown Primary Origin with a Long-term Survival after Surgery Alone.

An 80-year-old woman was referred to our hospital for a thorough examination of enlarged lymph nodes on the lesser curvature of the stomach. Upon suspicion of malignant lymphoma, the patient underwent open lymphadenectomy and was diagnosed with lymph node metastasis of poorly differentiated adenocarcinoma. The patient was subsequently diagnosed with microsatellite instability-high cancer of unknown primary origin. Surgical removal of the affected lymph nodes achieved full remission. Chemotherapy was considered in case of recurrence or identification of the primary site. Recurrence has not occurred in three years since the surgery. However, a long-term survival without chemotherapy is rare.